This invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to a stacked DRAM capacitor.
In recent years, as more and more circuit components have been squeezed into semiconductor integrated circuits, the minimum work dimensions have been getting smaller and the size of memory cells has been decreasing. As a result, the capacitor area in a memory cell has become very small. A decrease in the memory cell area results in a decrease in the capacity of the capacitor (storage capacity: Cs). The capacity of the capacitor has to be greater than a specific value from the viewpoints of sensitivity, soft errors, and noise in circuits.
The following two methods of increasing the capacity of a capacitor have been examined. A first method is to make the surface area of a capacitor as large as possible by forming the capacitor three-dimensionally. A second method is to use a high-permittivity insulating film (what is called a high E film) as a capacitor insulating film.
After the generations of design rules of 0.15 microns or less (or after the 1-GB DRAM generation), the processing of complex three-dimensional storage node electrodes (SN electrodes) has become increasingly difficult. Therefore, the method of using a high-permittivity insulating film as a capacitor insulating film is very important in making the capacity of a capacitor greater.
A typical high-permittivity insulating film is a (Ba, Sr) TiO3 (hereinafter, abbreviated as BST) film. For use of a BST film, the idea of using an Ru film, whose oxide is conductive (e.g., an RuO2 film is conductive), or a stacked film of RuO2 film/Ru film as an SN electrode has been examined (see S. Yamamichi, et al., xe2x80x9cTechnical Digest,xe2x80x9d IEDM, 1995, pp. 119-122). Hereinafter, a stacked DRAM capacitor having such a structure will be explained by reference to FIG. 37.
First, element isolating regions 102 are formed at the surface of a p-type Si substrate 101. Thereafter, a gate insulating film 103a, a gate electrode (a polycrystalline silicon film 103b and a WSi film 103c), an SiN film 104, a source/drain diffused layer 105, an SiN film 106, and an interlayer insulating film 108 are formed.
Next, polycrystalline silicon films 107a and 107b are embedded in an SN electrode contact region and a bit-line contact region. Thereafter, interlayer insulating films 109 and 111 are formed and a bit line 110 and an SN contact are formed.
Then, a TiSiX film 113, a TiN film 114, an Ru film 115, and an RuO2 film 116 are stacked. These stacked layers are patterned by normal lithographic techniques and RIE techniques to form an SN electrode. Thereafter, a high-permittivity insulating film 117, such as a BST film, is formed and then an upper electrode 118 (e.g., a stacked layer film of TiN film/Al film) is formed.
When the SN electrode is formed by the above conventional manufacturing method, the following problems arise.
When the SN electrode is formed by ordinary lithographic techniques and RIE techniques, the top corners of the SN electrode have right angles (or sometimes acute angles). This permits an electric field to concentrate at the top corners, resulting in an increase in leakage current in the capacitor insulating film. As a result of the SN electrode being patterned by RIE techniques, roughness of the side faces of the resist are amplified and transferred to the side faces of the SN electrode. The roughness of the side faces of the SN electrode increases leakage current in the capacitor insulating film.
Furthermore, the formation of the SN electrode by lithographic techniques makes the SN electrode liable to shift in position. Therefore, when the capacitor insulating film is formed, part of the plug can be exposed. Consequently, in forming a BST film serving as a capacitor insulating film, the metal plug can be oxidized. The oxidization of the metal plug would cause the following problems: a poorer electrical connection between the SN electrode and the plug and the plug film more liable to come off due to volume expansion caused by oxidation. To overcome these problems, a method of forming a barrier metal layer on the surface of the plug has been proposed. This method, however, has the following problems: the barrier metal has insufficient resistance to oxidation and the number of processes of manufacturing the barrier metal layer increases.
Moreover, when the SN electrode is formed on the plug and insulating film, it is desirable that such an SN electrode material should be used as has not only good electrical connection with the plug but also good adhesion to the insulating film. However, it is difficult to form an SN electrode that meets both of the requirements.
As described above, the conventional stacked DRAM capacitor has several problems stemming from the structure of the SN electrode and the manufacturing method and is not necessarily acceptable in terms of the electrical characteristics and reliability of the capacitor.
It is, accordingly, an object of the present invention to provide a semiconductor device with capacitors excellent in electrical characteristics and reliability and a manufacturing method thereof.
According to a first aspect of the present invention, there is provided a semiconductor device with a charge holding capacitor, the capacitor comprising, a lower electrode connected to one of the source and drain of an MIS transistor; a capacitor insulating film formed on the top face and side faces of the lower electrode; and an upper electrode formed on the capacitor insulating film, wherein the side faces of the lower electrode are so formed that they widen gradually as they go downward, and the side faces near the bottom of the lower electrode are in contact with an insulating film different from the capacitor insulating film.
With the invention, since the side faces of the lower electrode (corresponding to a storage node electrode) are so formed that they widen gradually as they go downward, the top corners of the lower electrode have an obtuse angle. This alleviates the concentration of electric field at the top corners, reducing leakage current in the capacitor insulating film. The improved coverage of the capacitor insulating film promotes the thinning of the capacitor insulating film, which increases the capacity of the capacitor. Furthermore, the uniformity of the film thickness of the upper electrode (corresponding to the plate electrode) is improved, providing the stable capacitor. Moreover, the increased side face area of the lower electrode increases the capacity of the capacitor.
In the first aspect of the invention, the side faces near the bottom of the lower electrode are in contact with the insulating film different from the capacitor insulating film. When the side faces of the lower electrode are so formed that they widen gradually as they go downward, the bottom corners of the lower electrode have an acute angle, which may permit an electric field to concentrate there. In the first aspect of the invention, because the insulating film is in contact with the bottom corners, the leakage current in the capacitor insulating film caused by the concentration of electric field is suppressed.
As described above, with the first aspect of the invention, not only does leakage current in the capacitor is reduced, but the capacity of the capacitor is also increased. Consequently, it is possible to provide a stacked DRAM excellent in reliability and characteristics.
According to a second aspect of the invention, there is provided a method of manufacturing semi-conductor device, comprising: the step of forming an insulating film on a substrate in which an MIS transistor has been formed; the step of removing part of the insulating film to make a hole whose side faces widen gradually as they go downward; the step of embedding in the hole a conducting film that is connected to one of the source and drain of the MIS transistor and is to make a lower electrode of a capacitor; the step of removing the insulating film to expose at least part of the side faces of the conducting film; the step of forming a capacitor insulating film on the top face of and the exposed side faces of the conducting film; and the step of forming an upper electrode of the capacitor on the capacitor insulating film.
In the second aspect of the invention, because the lower electrode is formed by embedding the conducting film in the hole made in the insulating film, the side faces of the lower electrode are made flat and smooth. This prevents roughness of the side faces of the lower electrode from increasing leakage current in the capacitor insulating film.
In the second aspect of the invention, the step of removing part of the insulating film to make a hole whose side faces widen gradually as they go downward may includes: the step of making a first hole whose side faces widen gradually as they go downward by removing part of the insulating film; and the step of making a second hole by etching the insulating film in which the first hole has been made to enlarge the first hole.
Because the lower electrode is formed in the second hole made by enlarging the first hole, the dimensions of the lower electrode are greater than the dimensions determined by lithography. As a result, the surface area of the lower electrode is increased, which increases the capacity of the capacitor.
According to a third aspect of the invention, there is provided a semiconductor device with a charge holding capacitor, the capacitor comprising, a lower electrode connected to one of the source and drain of an MIS transistor; a capacitor insulating film formed on the top face and side faces of the lower electrode; and an upper electrode formed on the capacitor insulating film, wherein the side faces near the bottom of the lower electrode are recessed and the recessed portions are in contact with an insulating film different from the capacitor insulating film.
In the third aspect of the invention, the insulating film has eaten into the recessed portions of the side faces near the bottom of the lower electrode. Consequently, the adhesion of the lower electrode to the underlying region is improved, as compared with the case where the whole bottom surface of the lower electrode is formed on the flat surface. This makes it possible to construct a highly reliable stacked DRAM.
In the third aspect of the invention, the side faces higher than the recessed portions of the lower electrode may be so formed that they widen gradually as they go downward.
This structure not only decrease leakage current in the capacitor but also increase the capacity of the capacitor. Therefore, it is possible to provide a stacked DRAM excellent in reliability and characteristics.
According to a fourth aspect of the present invention, there is provided a method of manufacturing semiconductor device, comprising: the step of forming a first insulating film on a substrate in which an MIS transistor has been formed and a second insulating film on the first insulating film; the step of removing part of the first and second insulating films to make a first hole; the step of forming a second hole by selectively etching the second insulating film with reference to the first insulating film to enlarge the upper portion of the first hole; the step of embedding in the second hole a conducting film that is connected to one of the source and drain of the MIS transistor and is to make a lower electrode of a capacitor; the step of removing the second insulating film to expose at least part of the side faces of the conducting film; the step of forming a capacitor insulating film on the top face of and the exposed side faces of the conducting film; and the step of forming an upper electrode of the capacitor on the capacitor insulating film.
In the fourth aspect of the invention, because the lower electrode is formed by embedding the conducting film in the hole made in the insulating film, leakage current in the capacitor insulating film is prevented from increasing due to roughness of the side faces of the lower electrode, as in the second aspect of the invention. Furthermore, the lower electrode is formed in the second hole made by enlarging the first hole, which makes the dimensions of the lower electrode larger than the dimensions determined by lithography. As a result, the surface area of the lower electrode is increased, which increases the capacity of the capacitor.
According to a fifth aspect of the invention, there is provided a semiconductor device with a charge holding capacitor, the capacitor comprising, a lower electrode connected via a plug to one of the source and drain of an MIS transistor; a capacitor insulating film formed on the lower electrode; and an upper electrode formed on the capacitor insulating film, wherein a conducting film selected from a group consisting of a titanium nitride (TiN) film, a titanium aluminum nitride (TiAlN) film, a titanium silicon nitride (TiSiN) film, a tantalum silicon nitride (TaSiN) film, a ruthenium (Ru) film, an iridium (Ir) film, a stacked film of ruthenium film and ruthenium oxide film (the ruthenium oxide film is formed on the ruthenium film preferably), a stacked film of iridium film and iridium oxide film (the iridium oxide film is formed on the iridium film preferably), and a stacked film formed of any combination of these films (the titanium nitride film, the titanium aluminum nitride film, the titanium silicon nitride film, the tantalum silicon nitride film, the ruthenium film, the iridium film, the stacked film of ruthenium film and ruthenium oxide film, the stacked film of iridium film and iridium oxide film) is formed between the lower electrode and the plug in such a manner that it self-aligns with the plug.
In the fifth aspect of the invention, the conducting film excellent in oxidation resistance, such as titanium aluminum nitride, has been formed between the lower electrode and the plug in such a manner that it self-aligns with the plug. This prevents the exposed portion of the plug from being oxidized in forming the capacitor insulating film. As a result, a highly reliable stacked DRAM can be constructed.
According to a sixth aspect of the invention, there is provided a semiconductor device with a charge holding capacitor, the capacitor comprising, a lower electrode connected via a plug to one of the source and drain of an MIS transistor; a capacitor insulating film formed on the lower electrode; and an upper electrode formed on the capacitor insulating film, wherein a conducting film obtained by nitriding the plug is formed between the lower electrode and the plug in such a manner it self-aligns with the plug.
As with the fifth aspect of the invention, with the sixth aspect, the exposed portion of the plug is prevented from being oxidized in forming the capacitor insulating film. Use of the conducting film formed by nitriding the plug eliminates a lithographic process of forming the conducting film, simplifying the manufacturing processes.
According to a seventh aspect of the invention, there is provided a semiconductor device with a charge holding capacitor, the capacitor comprising, a lower electrode connected via a plug to one of the source and drain of an MIS transistor; a capacitor insulating film formed on the lower electrode; and an upper electrode formed on the capacitor insulating film, wherein the lower electrode includes a first conducting portion formed on the plug in such a manner that it self-aligns with the plug, and a second conducting portion formed on the side faces of or the side faces and top face of the first conducting portion.
In the seventh aspect of the invention, the first conducting portion is so formed that it self-aligns with the plug. This provides a good electrical connection between the lower electrode and the plug. Furthermore, the exposed portion of the plug is prevented from being oxidized in forming the capacitor insulating film.
According to an eighth embodiment of the invention, there is provided a method of manufacturing semi-conductor device, comprising: the step of forming an insulating film with a hole on a substrate in which an MIS transistor has been formed; the step of forming in the hole a plug connected to one of the source and drain of the MIS transistor in such a manner that the top face of the plug is positioned between the top and the bottom of the hole; the step of forming a first conducting film on the plug in the hole; the step of exposing at least part of the side faces of the first conducting film by removing part of the insulating film; the step of forming a second conducting film on the exposed side faces of or the exposed side faces and top face of the first conducting film; the step of forming a capacitor insulating film on a lower electrode of a capacitor composed of the first and second conducting films; and the step of forming an upper electrode of the capacitor on the capacitor insulating film.
According to a ninth aspect of the invention, there is provided a semiconductor device with a charge holding capacitor, the capacitor comprising, a lower electrode connected via a plug to one of the source and drain of an MIS transistor; a capacitor insulating film formed on the lower electrode; and an upper electrode formed on the capacitor insulating film, wherein the lower electrode includes a first constituting portion that is embedded in a hole in which the plug has been embedded and so formed that it self-aligns with the plug and a second constituting portion which is formed on the first constituting portion and on regions outside the fist constituting portion and whose cross section is larger than that of the first constituting portion, the first constituting portion and the second constituting portion being formed integrally by a continues film.
In the ninth aspect of the invention, the first constituting portion of the lower electrode is so formed that it self-aligns with the plug. This provides a good electrical connection between the lower electrode and the plug. Furthermore, the exposed portion of the plug is prevented from being oxidized in forming the capacitor insulating film. Moreover, because the first and second constituting portions are formed integrally by the continuos film, the adhesion of the lower electrode to the underlying region is improved, which provides a stacked DRAM excellent in reliability and characteristics.
In the ninth aspect of the invention, the side faces near the bottom of the second constituting portion of the lower electrode may be in contact with an insulating film different from the capacitor insulating film.
In the ninth aspect of the invention, the second constituting portion of the lower electrode may be so formed that the side faces widen gradually as they go upward.
In the ninth aspect of the invention, the second constituting portion of the lower electrode is so formed that the side faces widen gradually as they go downward.
According to a tenth aspect of the invention, there is provided a method of manufacturing semi-conductor device, comprising: the step of forming a first insulating film with a first hole on a substrate in which an MIS transistor has been formed; the step of forming in the first hole a plug connected to one of the source and drain of the MIS transistor in such a manner that the top face of the plug is positioned between the top and the bottom of the first hole; the step of forming a second insulating film with a second hole, the second hole being formed on a region corresponding to the first hole and on regions outside the first hole; the step of embedding a conducting film on the plug in the first hole and in the second hole; the step of exposing at least part of the side faces of the conducting film by removing the second insulating film; the step of forming a capacitor insulating film on the lower electrode of a capacitor composed of the conducting film; and the step of forming the upper electrode of the capacitor on the capacitor insulating film.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.